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Smart enclosure designers keep their cool

28Feb

The life expectancy of control system components typically decreases with increasing temperature. Adopting a whole life costing approach to the selection of cooling units can help to reduce associated costs as well as the risk of premature component failure resulting from high enclosure temperatures

Careful planning using modern technologies - including computational fluid dynamics to assess the cooling requirements of proposed electrical enclosures, and thermography to visualise the thermal performance of functioning electrical enclosures - can aid enclosure design and the help the enclosure designer select a climate control system appropriate to his or her application. Software, such as Rittal’s ‘Therm’ was developed for this purpose, facilitating the selection of appropriate and correctly dimensioned climate control equipment, and allowing the user to solve a cooling quandary quickly without having to resort to laborious calculations.

Selecting an appropriate cooling unit and ensuring that it is installed correctly is not simply a case of demonstrating best practice, it can also lead to reduced operating costs, increased life expectancy and improved cooling performance. An oversized cooling unit is not only inefficient in terms of energy usage, but may also result in an increased number of compressor switching cycles, adversely affecting its service life. Should the airflow be restricted, either through the internal or the external air path of the cooling unit, then the distribution of cooled air throughout the enclosure and its ability to dissipate heat may be compromised.

When sizing a cooling system, it is also imperative that the heat dissipated by the installed equipment, the actual ambient temperature and the most favourable operating temperature for the installed equipment, are all fully understood. Exaggerating the cooling requirement using an arbitrarily selected maximum temperature inside the enclosure, which is lower than that required, and over-estimating the maximum ambient temperature, may lead to oversized cooling equipment that does not operate efficiently. Moreover, the possibility that ambient air may be sufficient for cooling purposes is likely to be overlooked altogether.

Another important point to consider is the extent to which the enclosure prevents air leakage. A sealed enclosure - one that satisfies an ingress protection category rating of IP54 - minimises the amount of energy that is wasted due to cooled air escaping from the enclosure. And a cooled sealed enclosure produces a lower level of condensate, which must either be drained or collected and regularly disposed of.

Maintenance and energy efficiencyHaving correctly selected and installed the required cooling products, it is crucial these are properly maintained so that both cooling performance and energy consumption levels are preserved. Regular cleaning or replacement of filters is essential to ensure that the airflow through the enclosure does not decrease; and if a condensate drain is not installed, the regular emptying of condensate collecting bottles adds to the maintenance task. Clearly, these activities are time-consuming and expensive - but help is at hand. Nano-coated condenser coils and integral electrical condensate evaporation remove the need for filters (in all but the most contaminated environments) as well as condensate drains and reservoirs, significantly reducing maintenance requirements.

A number of technological advances can also be employed to improve the energy efficiency of climate control equipment. The diagonal fan technology, used in fan-and-filter units, for example, provides improved performance against increased static pressure difference, which, in turn, provides a more constant air throughput, effectively minimising the occurrence of hot spots within the enclosure.

Use of the latest compressor technology and electronically commutated fans, the optimum arrangement of heat exchangers and an optimised refrigerant volume all contribute towards a reduction in energy consumption. Cooling unit ranges that have been specifically developed to minimise the use of energy, such as the Rittal TopTherm Blue e, utilise all of these technologies to achieve energy savings of up to 45%.

Intelligent controlIn addition to these energy saving and maintenance reducing technologies, there are software products that can also be used to reduce the energy consumption of cooling products. Rittal’s Eco-mode control system, for example, features an intelligent strategy that switches off the internal fan when the temperature inside the enclosure falls to 10K below the level desired. The fan is then enabled for a period of 30 seconds every 10 minutes to ensure the accuracy of the sensed temperature before being permanently enabled when the temperature rises to 5K below the set point temperature. Eco-mode may be incorporated into a number of products, including cooling units and heat exchangers.

There may be instances where there is a demand for cooling other than that of the control system, such as the temperature control of a process coolant. In such cases, it may be more economical to consider a combination of air/water heat exchangers and a remote chiller unit. This type of installation allows heat to be removed from the volume in which it is generated to an environment where the impact of its dissipation is less noticeable or undesirable. Since heat may be dissipated externally, it is possible to take advantage of free cooling, which uses the outside ambient air to cool the heated water by means of a separate condenser and the existing fans and pumps that are integrated into the chilled water circuit.

Data centresCost effective climate control is not purely the domain of industry. Continued pressure on data centre managers to improve their power usage effectiveness (PUE), for example, has seen the quest for energy savings steadily gaining ground in the IT sector as well. Energy efficiency aside, it is also an essential task of the data centre manager to maintain a properly controlled temperature environment for computing hardware. A rise of 10K above room temperature will result in a reduction of 50% in the mean-time-between-failure of such equipment.

Introducing a water-cooling system not only solves the heat issues associated with high density computing, it also has the effect of improving cooling efficiencies. Cooling using chilled water supplied by free cooling chillers also has the additional benefit of reducing cooling energy operating costs by at least 50%. It is estimated that 100% free cooling (using ambient air) is available for nearly 70% of the year within the UK. Examples of water-cooled climate control products available for use with server racks include computer room air conditioning (CRAC) systems and liquid cooling packages (LCP).

Hot aisle cold aisle systems are a traditional method of delivering cold air to the servers within a data centre. Cold air is provided by the CRAC system via the floor void into the cold aisle and pulled into the server inlet. Hot air from the server outlet is drawn into the CRAC system via the hot aisle. However, this system typically needs the CRAC system to be oversized by 30% to ensure that there is sufficient air available and adequate redundancy within the system, which reduces the system overall efficiency.

One of the key issues with hot aisle cold aisle systems is that the hot and cold air are allowed to mix and therefore the temperature of the air returning to the inlet of the CRAC system is reduced and, as a consequence, so is the cooling output. Cold aisle containment (CAC), which prevents the mixing of the hot exhaust air and the cold supply air by simply adding doors at each end and roof panels across the top of the aisle, has been developed specifically to address this issue.

Even for a site where there is no false floor, CAC should not be immediately dismissed. By introducing an LCP, which is essentially an air-water heat exchanger that can be fitted either as an extension to, or inside the rack, and which is capable of providing up to 60kW of cooling per module, the need for a CRAC system - and hence a false floor - is removed.

So, whether your climate control requirement is for an industrial or IT sector application, there is a cooling system available that will not only satisfy your thermal requirements but which will also reduce your costs and improve your carbon footprint.